Very cool website -- features real-time tracking of flights in North America by Flight number, type of Airplane, Airport. It also has historical data and analysis of traffic.
I present FlightAware
Here is a real-time chart of all the airplanes leaving or coming into Bellingham International Airport at 8:30PM today:
Click for full-size Image
It aggregates data available from FAA online sources and compiles it into this wonderful resource. They are supporting themselves with Google advertising and offering customized commercial services.